diff options
Diffstat (limited to 'src/include/nodes/relation.h')
| -rw-r--r-- | src/include/nodes/relation.h | 33 |
1 files changed, 27 insertions, 6 deletions
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h index e305870aa7b..416cdb0c55b 100644 --- a/src/include/nodes/relation.h +++ b/src/include/nodes/relation.h @@ -6,7 +6,7 @@ * * Copyright (c) 1994, Regents of the University of California * - * $Id: relation.h,v 1.34 1999/07/15 23:03:56 momjian Exp $ + * $Id: relation.h,v 1.35 1999/07/24 23:21:04 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -151,6 +151,23 @@ typedef struct Path List *loc_restrictinfo; } Path; +/*---------- + * IndexPath represents an index scan. Although an indexscan can only read + * a single relation, it can scan it more than once, potentially using a + * different index during each scan. The result is the union (OR) of all the + * tuples matched during any scan. (The executor is smart enough not to return + * the same tuple more than once, even if it is matched in multiple scans.) + * 'indexid' is a list of index relation OIDs, one per scan to be performed. + * 'indexqual' is a list of index qualifications, also one per scan. + * Each entry in 'indexqual' is a sublist of qualification expressions with + * implicit AND semantics across the sublist items. Each one of the sublist + * items must be an operator expression of the form (var op something) or + * (something op var), where the var is a field the associated index keys on + * and the op is a member of the operator class of the index. + * NOTE that the semantics of the top-level list in 'indexqual' is OR + * combination, while the sublists are implicitly AND combinations! + *---------- + */ typedef struct IndexPath { Path path; @@ -205,16 +222,20 @@ typedef struct JoinKey } JoinKey; /* - * clause info + * Restriction clause info. + * We create one of these for each AND sub-clause of a restriction condition + * (WHERE clause). Since the restriction clauses are logically ANDed, we + * can use any one of them or any subset of them to filter out tuples, + * without having to evaluate the rest. The RestrictInfo node itself stores + * data used by the optimizer while choosing the best query plan. */ typedef struct RestrictInfo { NodeTag type; - Expr *clause; /* should be an OP clause */ - Cost selectivity; - bool notclause; - List *indexids; + Expr *clause; /* the represented subclause of WHERE cond */ + Cost selectivity; /* estimated selectivity */ + List *indexids; /* subclause index IDs if clause is an OR */ /* mergejoin only */ MergeOrder *mergejoinorder; |